1. Field of the Invention
The present invention relates to those articles of manufacture known as coated abrasives, which consist of flexible backings to which are adhered a plurality of abrasive grit particles on at least one side. Coated abrasives are used primarily for the shaping, dimensioning, or surface finish alteration of other material objects known generally as workpieces. Small particles of material removed from the workpieces and/or shed from the coated abrasives during working are collectively called swarf. In many cases, the swarf tends wholly or partially to adhere to the surface of the coated abrasive, eventually loading or clogging its abrasive surfaces and rendering it unsuited for further use. The invention relates particularly to coated abrasives which are specially resistant to such failure by loading.
2. Description of the Prior Art
A common commercial practice for the manufacture of coated abrasives which resist loading in the sanding of paints, primers, wood sealer coats, and a wide variety of other finishing compositions used on workpieces is essentially that described in U.S. Pat. No. 2,768,886 to Twombly. This patent describes the preparation of coated abrasives which have a final grit-side surface coating of unfused metallic soaps applied, preferably from a dispersion of such soap in a volatile liquid. The application of this metallic soap is done as a separate coating step in addition to the normal making and sizing coating steps which are customarily used for achieving adherence of the abrasive grits to the backing. In some cases, it may be possible to prepare products with adequate properties without using a sizing adhesive. The need for an additional coating operation compared with most coated abrasives obviously imposes labor and material costs.
Since the publication of the Twombly Patent, there have been several other patents directed to other types of "third" coatings, i.e., coatings in addition to the two normal making and sizing ones, which would achieve loading-resistant coated abrasives. Examples include polyvinylacetate as disclosed in Canadian Pat. No. 931,767 to Greenwood, polytetrafluoroethene and mixtures thereof as disclosed in U.S. Pat. No. 3,042,508 to Haigis, and mixtures of thermosetting resins, elastomers, and metallic soaps as disclosed in U.S. Pat. No. 3,619,150 to Rinker et al.
U.S. Pat. No. 3,043,673 to Klein et al. teaches the use of oxy-containing compounds either in a third coat or in the conventional sizing coat of a coated abrasive, together with an exceptionally high ratio of binder adhesive to grain, as an effective means for increasing the resistance of coated abrasives to loading in the finishing of leather and similar materials. The oxy compounds specified in this patent are all neutral organic compounds not expected to ionize in water solution. U.S. Pat. No. 3,089,763 to Gladstone teaches the use of polyoxyalkylene compounds in the size of coated abrasives, and one of the objects stated is to reduce loading. However, the teaching of the Gladstone patent is restricted to sizing compositions in which the principal constituent is an amine-catalyzed phenolic resin.